CN114985938B - A method for preparing superhydrophobic surface of aluminum alloy by flat-top laser peening - Google Patents

Abstract

The invention provides a method for preparing an aluminum alloy superhydrophobic surface by flat-top laser shot peening, comprising the following steps: pretreating the surface of the aluminum alloy; uniformly coating a nano-scale carbon powder layer on the surface of the pretreated aluminum alloy; Square spot flat-top nanosecond pulse laser, the carbon powder layer is used as the absorption layer, and the aluminum alloy surface is subjected to unconstrained layer shot peening, and the beam is always kept perpendicular to the aluminum alloy surface; after the shot peening, the residual carbon powder is removed and passed Low-temperature heat treatment reduces the surface energy of the material, and a superhydrophobic aluminum alloy surface with a micro-nano multilevel structure is obtained. The invention increases the content of carbon element near the surface of the aluminum alloy material, and can effectively improve the hardness and wear resistance of the prepared hydrophobic surface.

Description

A method for preparing superhydrophobic surface of aluminum alloy by flat-top laser peening

technical field

The invention relates to the field of preparation of superhydrophobic surfaces of aluminum alloys, in particular to a method for preparing superhydrophobic surfaces of aluminum alloys by flat-top laser peening.

Background technique

Aviation aluminum alloy is light in weight, high in strength, good in toughness, has excellent mechanical properties and processing properties, and is widely used in aviation and aerospace fields. The surface of aviation aluminum alloy has high wettability, which causes water droplets to adhere and condense in a low-temperature and humid working environment. The surface of the material is prone to corrosion and freezing, which will adversely affect the service life and performance of aluminum alloy components. A large number of studies have shown that the construction of superhydrophobic structures on the surface of aerospace aluminum alloys can effectively slow down the corrosion and icing of the material surface. Therefore, the preparation of superhydrophobic surfaces of aluminum alloys is of great significance in the field of aviation and aerospace.

At present, there are many methods for preparing superhydrophobic surface of aluminum alloy materials, such as electrochemical method, EDM method, chemical etching method, electroplating method, sol-gel method, etc., but these preparation methods have many defects. For example, the process is complex and inefficient, some of which require special equipment and harsh preparation environments, making the preparation of super-hydrophobic surfaces expensive, the prepared hydrophobic texture has low strength, poor mechanical stability, and the strength of the matrix material after preparation. This greatly limits the application of superhydrophobic surface preparation technology on aerospace aluminum alloy components with complex and harsh service environments.

As a new type of surface modification and strengthening process, laser peening technology uses the plasma shock wave generated by laser irradiation on the surface of the material to make beneficial changes in the microstructure of the material near the surface, and at the same time induces high-amplitude residual compressive stress inside the matrix. , so that the mechanical properties of the material are effectively improved, and it has the advantages of high strengthening efficiency and strong controllability. Using the thermal-mechanical coupling effect produced by laser peening can produce porous micro-nano multi-level structure on the surface of aerospace aluminum alloy, and endow the aluminum alloy surface with superhydrophobicity after reducing the surface energy, which is an important superhydrophobic surface preparation method. However, the current process of laser peening to prepare superhydrophobic surface of aluminum alloy adopts circular Gaussian spot without absorbing layer for shot peening, which is affected by Gaussian circular spot and overlap rate during shot peening, so that the prepared superhydrophobic macroscopic surface has With certain undulations, the rolling resistance of the droplets increases, which is not conducive to the sliding of the droplets away from the surface of the material, and has limited ability to improve the strength of the prepared hydrophobic texture.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a method for preparing a superhydrophobic surface of an aluminum alloy by flat-top laser peening. On the basis of the existing technology for preparing a superhydrophobic surface by laser peening, a flat-top laser with a square spot is selected. , the carbon powder layer is used as the absorbing layer for unconstrained layer shot peening. On the one hand, the laser irradiation increases the absorption rate of laser energy on the carbon powder layer, and a part of the carbon powder absorbs the laser energy and converts into plasma, and the plasma rapidly The shock wave generated by the expansion will stir and modulate the heated and melted carbon powder and the remelted material on the surface of the aluminum alloy, increasing the content of carbon elements near the surface of the aluminum alloy material, which can effectively improve the hardness and wear resistance of the prepared hydrophobic surface; another On the one hand, the thermal-mechanical coupling effect produced by laser peening produces a porous micro-nano multi-level structure with a hydrophobic effect on the surface of the aluminum alloy, and at the same time effectively strengthens the microstructure of the matrix material and improves the mechanical properties. Among them, the square spot flat-top pulse laser is used as the light source of laser shock, which can effectively change the undulating shape of the circular spot Gaussian laser peening, improve the surface flatness, effectively reduce the sliding resistance of the droplet, and further improve the prepared surface. superhydrophobic effect. Therefore, the present invention uses the carbon powder layer as the absorbing layer to perform unconstrained layer square spot flat-top pulse laser peening, and efficiently completes the preparation of the super-hydrophobic surface on the aluminum alloy substrate while realizing the strengthening of the substrate material, super-hydrophobic effect and surface strength. It is also effectively improved, and the mechanical wear resistance of the superhydrophobic surface is enhanced.

The present invention achieves the above-mentioned technical purpose through the following technical means.

A method for preparing an aluminum alloy superhydrophobic surface by flat-top laser peening, comprising the following steps:

Pretreatment of aluminum alloy surface;

Evenly coat the nano-scale carbon powder layer on the surface of the pretreated aluminum alloy;

Using a square spot flat-top nanosecond pulse laser, the carbon powder layer is used as an absorbing layer, and the surface of the aluminum alloy is subjected to unconstrained layer shot peening, and the beam is always kept perpendicular to the surface of the aluminum alloy;

After shot peening, the residual carbon powder is removed, and the surface energy of the material is reduced by low-temperature heat treatment to obtain a superhydrophobic aluminum alloy surface with a micro-nano multi-level structure.

Further, the pretreatment includes: grinding and polishing the surface of the aluminum alloy step by step to make the surface roughness ≤ 50 μm, ultrasonically cleaning and drying the treated surface with deionized water.

Further, the nanoscale carbon powder layer is a mixture of nanoscale carbon powder and epoxy resin glue, the diameter of the nanoscale carbon powder ranges from 50 nm to 300 nm, and the thickness of the nanoscale carbon powder layer is 100 μm to 500 μm.

Further, the flat-top nanosecond pulsed laser with a square spot is obtained by passing a circular flat-top nanosecond pulsed laser through a beam shaper.

Further, the laser that produces flat-top nanosecond pulse laser with square spot is Nd:YAG solid-state laser, and the laser processing parameters are: wavelength 1064nm, laser energy 1J~15J, repetition frequency 1Hz~5Hz, pulse width 10ns~20ns, square spot side length Size≤5mm.

Further, the method for lowering the surface energy of the material by the low-temperature heat treatment is as follows: placing the aluminum alloy material after the shot blasting treatment in a vacuum drying oven at 80° C. to 150° C. for 1 h to 10 h.

The beneficial effects of the present invention are:

1. The method for preparing the superhydrophobic surface of aluminum alloy by flat-top laser shot peening of the present invention selects square spot flat-top pulse laser for use. Compared with the traditional circular spot Gaussian pulse laser in the shot peening process, the stress wave propagates in the longitudinal direction Based on this feature, the residual stress field induced by each adjacent shot peening point of the square flat-top spot laser peening will not produce complex interference. , the inhomogeneity of the stress-strain field caused by the sequence of shot peening will be greatly weakened, avoiding the stress cavity phenomenon caused by circular spot Gaussian pulse laser peening, and the macroscopic surface morphology after shot peening is relatively flat, which is conducive to improving the preparation The hydrophobic effect of the surface, and the distribution of the residual compressive stress field of the matrix material is more uniform, and the service life of the material is prolonged.

2. The method for preparing the superhydrophobic surface of aluminum alloy by flat-top laser peening according to the present invention uses a carbon powder layer as the absorbing layer during laser peening, when the intense pulsed laser radiation with high power density is irradiated on the surface of the aluminum alloy sheet At this time, the carbon powder absorbs part of the energy to cause rapid ionization and gasification, and continues to absorb laser energy to generate high-voltage shock waves to stir and modulate the melted carbon powder and the remelted material on the surface of the aluminum alloy. The carbon content near the surface of the aluminum alloy increases, effectively improving the hydrophobic micro The hardness of the nanotexture makes the prepared superhydrophobic surface have better wear resistance; at the same time, under the effect of laser peening force, the surface layer of the metal material forms a higher dislocation density, and the grains are also effectively The refined, textured surface has improved friction and wear properties and mechanical stability.

3. The method for preparing an aluminum alloy superhydrophobic surface by flat-top laser peening according to the present invention uses a low-temperature heat treatment process to reduce the surface energy of a surface with a micro-nano multi-level structure, which is clean and pollution-free. The low-temperature heat treatment makes the surface of the sample fully interact with the oxygen in the air, regulates the composition of the surface of the micro-nano multi-level structure, and significantly improves the adsorption capacity of the aluminum alloy surface to the organic matter in the air. The introduction of a large amount of carbon elements in the nanoscale texture increases the non-polar functional groups on the surface of the material, effectively reduces the surface energy, and realizes the preparation of the superhydrophobic surface of the fluorine-free aluminum alloy.

4. The method for preparing the superhydrophobic surface of aluminum alloy by flat-top laser peening according to the present invention has the advantages of simple and convenient operation, low cost, etc., is easy to realize large-scale industrial production, and significantly improves the micro-nano multi-level texture of the superhydrophobic surface. Wear resistance and mechanical stability, and the strength of the aluminum alloy matrix material have also been improved to a certain extent, which is better suitable for the complex and harsh environment in the aerospace field, and has a wide range of industrial application prospects.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. For some embodiments, it is obvious to those skilled in the art that other drawings can be obtained based on these drawings without any creative effort.

Fig. 1 is a schematic diagram of the method for preparing an aluminum alloy superhydrophobic surface by flat-top laser peening according to the present invention.

Fig. 2 is an actual effect diagram of the superhydrophobic surface morphology prepared in Example 1 of the present invention.

Fig. 3 is a comparison diagram of contact angles of droplets on superhydrophobic surfaces prepared in various embodiments of the present invention.

Fig. 4 is a comparison chart of microhardness of superhydrophobic surfaces prepared in various embodiments of the present invention.

Fig. 5 is a graph showing the variation of droplet contact angles of the superhydrophobic surface prepared in Example 3 of the present invention after ultrasonic vibration treatment for different durations.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

In describing the present invention, it is to be understood that the terms "central", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "axial", The orientation or positional relationship indicated by "radial", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description , rather than indicating or implying that the device or element referred to must have a particular orientation, be constructed and operate in a particular orientation, and thus should not be construed as limiting the invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. Thus, a feature defined as "first" and "second" may explicitly or implicitly include one or more of these features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

In the present invention, unless otherwise clearly specified and limited, terms such as "installation", "connection", "connection" and "fixation" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection , or integrally connected; it may be mechanically connected or electrically connected; it may be directly connected or indirectly connected through an intermediary, and it may be the internal communication of two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

As shown in Figure 1, the method for preparing an aluminum alloy superhydrophobic surface by flat-top laser peening of the present invention comprises the following steps:

The surface of the aluminum alloy is polished and polished step by step to make the surface roughness ≤ 50 μm, and the treated surface is ultrasonically cleaned and dried with deionized water;

Mix and coat nano-carbon powder with a diameter ranging from 50nm to 300nm and epoxy resin glue on the surface of the aluminum alloy plate to form a nano-scale carbon powder layer with a thickness of 100 μm to 500 μm on the surface of the aluminum alloy;

Using a square spot flat-top nanosecond pulse laser, selecting reasonable parameters and paths, using the carbon powder layer as the absorbing layer during laser peening, performing unconstrained layer shot peening on the surface of the aluminum alloy sample, and the beam is always kept in line with The surface of the plate is vertical;

After the shot peening, use ultrasonic cleaning to remove the residual carbon powder on the surface of the aluminum alloy, and then place the shot peened plate in a vacuum drying oven with a constant temperature of 80°C to 150°C for low temperature treatment for 1h to 10h to reduce the material Surface energy, complete the preparation of superhydrophobic aluminum alloy surface with micro-nano multi-level structure.

The method for preparing the superhydrophobic surface of aluminum alloy by flat-top laser peening described in the present invention converts the circular spot flat-top nanosecond pulse laser into a square spot flat-top nanosecond pulse laser through a beam shaper, and uses nano-scale carbon powder layer For the absorbing layer, unconstrained layer laser peening is performed on the surface of the aluminum alloy, combined with a low-temperature heat treatment process to reduce the surface energy of the material, and endow the aluminum alloy surface with superhydrophobicity. The use of square-spot flat-top pulsed laser for peening is beneficial to control the residual compressive stress generated by laser peening, making the stress distribution more uniform and effectively improving the service life of materials; when using nano-scale carbon powder as the Absorbing layer, the absorption rate of laser energy is increased to generate high-intensity plasma shock waves, which can impact the material while stirring the melted carbon powder and the remelted material on the surface of the aluminum alloy, greatly increasing the content of carbon elements on the surface of the aluminum alloy. In turn, the strength and hardness of the prepared multi-level micro-nano structure are improved, so that the prepared superhydrophobic surface has high matrix wear resistance and mechanical stability; The optimal setting of parameters such as laser peening can realize the regulation and control of the macroscopic morphology of the superhydrophobic surface prepared by laser peening, so that the prepared surface is relatively flat, which can effectively reduce the resistance of the droplet sliding, and the rolling angle is reduced; in the present invention, low temperature heat treatment is used The treatment method introduces a large number of non-polar functional groups on the surface of the aluminum alloy material, which reduces the surface energy of the prepared micro-nano multi-level structure, and realizes the preparation of the superhydrophobic surface of the aluminum alloy by adopting a method without fluorine addition.

In order to make the purpose, technical solution and advantages of the present invention clearer, 2024-T351 aviation aluminum alloy is selected as the research object below, and the present invention will be described in detail in conjunction with specific examples.

Embodiment one:

The method for preparing the superhydrophobic surface of aluminum alloy by flat-top laser peening described in embodiment one may further comprise the steps:

(1) Grind the surface of 2024-T351 aviation aluminum alloy with 400#, 800#, 1000#, 1500#, 2000# grain size sandpaper, and polish it on a grinding and polishing machine, so that the surface of the aluminum alloy material reaches a mirror surface (Ra ≤50μm), then ultrasonically clean the surface of the sample in absolute ethanol solution for 5 minutes, and dry it in a vacuum drying oven for later use;

(2) Mix carbon powder with a diameter of 50 nm and epoxy resin glue on the surface of the aluminum alloy plate, and form a nano carbon powder layer with a thickness of 100 μm on the surface of the aluminum alloy;

(3) Select Nd:YAG high-repetition frequency and high-energy nanosecond pulse laser, adjust the beam shaper, so that the circular spot flat-top pulse nanosecond laser is transformed into a square spot flat-top pulse nanosecond laser. The specific parameters of laser peening are: Wavelength 1064nm, laser frequency 1Hz, pulse width 20ns, spot overlap rate 0%, spot diameter 3mm, laser energy 5J;

(4) After laser peening, use ultrasonic cleaning to remove residual carbon powder on the surface of the aluminum alloy, place the aviation aluminum alloy sample in a drying oven at a temperature of 100°C for 5 hours of low-temperature heat treatment, and introduce a large amount of carbon powder on the surface of the aluminum alloy material The non-polar functional group reduces the surface energy of the aluminum alloy material and completes the preparation of the superhydrophobic surface of the aluminum alloy.

The morphology of the superhydrophobic surface of the aerospace aluminum alloy prepared in Example 1 is shown in Figure 2. Compared with the superhydrophobic surface of the aluminum alloy prepared by the circular spot Gaussian pulse nanosecond laser, the macroscopic surface of the sample is relatively flat and has excellent microscopic properties. The nanoscale structure morphology improves the hydrophobic effect of the prepared surface; as shown in Figure 3, the surface of the sample prepared in Example 1 has excellent superhydrophobicity, the droplet sliding resistance is small, and the droplet contact angle is 162° , the rolling angle is 4°; as shown in Figure 4, under the heat generated by laser peening, the carbon element in the surface layer of aviation aluminum alloy increases greatly, which greatly improves the microhardness of the superhydrophobic surface of the prepared aviation aluminum alloy. It has reached 191HV, which is 46.9% higher than the average hardness value of 130HV on the surface of the untreated sample, which is of great significance for improving the wear resistance of the prepared superhydrophobic surface.

Embodiment two

On the basis of Example 1, the diameter of the carbon powder in Example 2 reaches 300 nm, the thickness of the carbon powder absorption layer is 500 μm, and the laser peening energy is set to 13J.

As shown in Figure 3, the droplet contact angle of the superhydrophobic surface obtained in Example 2 is 159°, and the rolling angle is 5°, which also realizes the excellent superhydrophobicity of the aerospace aluminum alloy surface. Embodiment 2 uses larger carbon powder particles and thicker carbon powder absorption layer, and the energy of laser peening is also increased. The deeper impact layer produced on the surface of aviation aluminum alloy, the strengthening effect is also effectively improved, as shown in the figure As shown in 4, the microhardness value of the superhydrophobic surface of the aerospace aluminum alloy prepared in this embodiment is 211HV, which is 62.3% higher than the average hardness of 130HV on the surface of the untreated sample base material. The average hardness HV191 of the sample surface increased by 10.5%. More carbon powder and greater laser energy made the carbon element and the remelted material on the aluminum alloy surface more fully stirred, and the hardness and mechanical stability of the superhydrophobic surface were further improved.

Embodiment three

On the basis of Example 1, the diameter of the carbon powder in Example 3 is 150 nm, the thickness of the carbon powder absorption layer is 300 μm, and the laser peening energy is set to 8J.

The droplet contact angle of the sample surface treated in Example 3 is 164°, and the rolling angle is 4°. The surface of the prepared aviation aluminum alloy sample also has excellent superhydrophobic properties. The aviation aluminum alloy superhydrophobic surface prepared in this example The microhardness value is 201HV, which is 54.6% higher than the average hardness of 130HV on the surface of the untreated sample base material. The sample prepared in Example 3 was placed on an ultrasonic vibration table to carry out a hydrophobic surface stability characterization experiment. As shown in Figure 5, as the vibration time increased, the droplet contact angle of the prepared superhydrophobic surface decreased, but 5 Hours later, it still remains above 155°, which shows that the prepared aerospace aluminum alloy superhydrophobic surface has high mechanical stability.

It should be understood that although this description is described according to various embodiments, not each embodiment only includes an independent technical solution, and this description of the description is only for clarity, and those skilled in the art should take the description as a whole , the technical solutions in the various embodiments can also be properly combined to form other implementations that can be understood by those skilled in the art.

The series of detailed descriptions listed above are only specific descriptions for feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiment or All changes should be included within the protection scope of the present invention.

Claims (6)

1. A method for preparing an aluminum alloy super-hydrophobic surface by flat-top laser shot blasting is characterized by comprising the following steps:

pretreating the surface of the aluminum alloy;

uniformly coating a nano-scale carbon powder layer on the surface of the pretreated aluminum alloy;

adopting square light spot flat-top nanosecond pulse laser, wherein the carbon powder layer is used as an absorption layer, carrying out unconstrained layer shot blasting treatment on the surface of the aluminum alloy, and keeping the light beam vertical to the surface of the aluminum alloy all the time; laser irradiation increases the absorptivity of laser energy on the carbon powder layer, a part of carbon powder absorbs the laser energy and then is converted into plasma, shock waves generated by the rapid expansion of the plasma enable the heated and melted carbon powder and the remelting material on the surface of the aluminum alloy to be stirred and modulated, and the carbon powder is used for improving the content of carbon elements near the surface layer of the aluminum alloy material;

and removing residual carbon powder after shot blasting, and reducing the surface energy of the material through low-temperature heat treatment to obtain the super-hydrophobic aluminum alloy surface with the micro-nano multilevel structure.

2. The method for preparing the aluminum alloy superhydrophobic surface by the flat-top laser peening as claimed in claim 1, wherein the pretreatment comprises: and step-by-step grinding and polishing are carried out on the surface of the aluminum alloy to enable the surface roughness value to be less than or equal to 50 mu m, and the treated surface is subjected to ultrasonic cleaning and drying by deionized water.

3. The method for preparing the aluminum alloy super-hydrophobic surface through flat-top laser peening according to claim 1, characterized in that the nano-scale carbon powder layer is a mixture of nano-carbon powder and epoxy resin glue, the diameter range of the nano-carbon powder is 50 nm-300 nm, and the thickness of the nano-scale carbon powder layer is 100 mu m-500 mu m.

4. The method for preparing the aluminum alloy superhydrophobic surface through the flat-top laser peening according to claim 1, wherein the square-spot flat-top nanosecond pulse laser is obtained by passing a round flat-top nanosecond pulse laser through a beam shaper.

5. The method for preparing the aluminum alloy superhydrophobic surface by flat-top laser peening according to claim 1, wherein a laser generating square spot flat-top nanosecond pulse laser is Nd: YAG solid laser, the laser processing parameters are as follows: the wavelength is 1064nm, the laser energy is 1J-15J, the repetition frequency is 1 Hz-5 Hz, the pulse width is 10 ns-20 ns, and the side length of the square light spot is less than or equal to 5mm.

6. The method for preparing the aluminum alloy super-hydrophobic surface by the flat-top laser peening according to claim 1, wherein the method for reducing the surface energy of the material by the low-temperature heat treatment is as follows: and (3) placing the aluminum alloy material subjected to shot blasting treatment in a vacuum drying oven at the temperature of 80-150 ℃ for treatment for 1-10 h.

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